The present invention relates to a photocurable composition, which is suitable for making photoresists, composite permselective membranes, and novel coatings.
A wide variety of photocurable compositions and photo-reactive materials are known in the prior art. Two main approaches exist in the art for producing photocurable compositions: (1) photocurable (photoinduced radical) compositions based upon polymerizable ethylenically unsaturated groups, and (2) photocurable compositions based upon photoacid generating compounds which function as photoinitiators for cationic polymerization. Both these approaches are reviewed in UV Curing; Science and Technology, S. P. Pappas, Editor, Technology Marketing Corporation, Norwalk, Conn. (1980). Illustrative ethylenically unsaturated compositions are described in U.S. Pat. Nos. 4,544,621: 4,564,580, 4,668,601, and 4,798,877. In one embodiment these photocurable compositions can comprise a photoinitiator, such as the onium compounds described in U.S. Pat. No. 4,632,891, and a polymerizable material which is activated by the photoinitiator. U.S. Pat. No. 4,229,519 discloses that polymers containing quaternary nitrogen groups bearing ethylenically unsaturated groups may be cured with radiation under nitrogen in the presence of a suitable photoinitiator.
Illustrative of photocurable compositions which comprise a photoacid generating initiator are those described in U.S. Pat. Nos. 4,081,276: 4,551,418 and 4,610,052. The most common photoacid generating systems are diaryliodonium and triarylsulfonium salts. Recent work in photoacid generating compounds are described in proceedings of ACS Division of Polymeric Materials, Science and Engineering, Vol. 61, Fall Meeting 1989, in Miami Beach, Fla. J. V. Crivello, "Chemistry of Photoacid Generating Compound", p. 62. Generally, these photocurable compositions are water incompatible and require organic solvents for preparation of coatings.
U.S. Pat. No. 4,118,297 describes aromatic cyclic sulfonium zwitterions which polymerize upon exposure to ultraviolet light. Japanese Kokai No. 34,445, published Feb. 28, 1983 describes photosensitive zwitterions of aryl cyclic sulfonium.
In conventional processes a photocurable composition is selectively exposed to actinic or other radiation in a desired pattern. The portions of the composition which are not subjected to radiation can be removed or developed by immersion in a suitable solvent. This is commonly referred to as a negative pnotoresist. In some applications, a photocurable composition is rendered more soluble by exposure to radiation and this photoreacted area is removed during developing. Such compositions are referred to as positive photoresists.
Photocurable compositions are commonly used to form lithographic printing plates, inks cured with ultraviolet (UV) radiation or printed circuits. After development of the image on the desired substrate, the exposed surface may be etched by conventional techniques. Similar techniques can be used to manufacture integrated circuits and other microelectronic components. However, photoresists used in such applications must afford a very high degree of resolution because of the fine detail required in these miniaturized images.
For accurate image formation in microlithographic applications it is desirable to have a relatively thin coating (typically about 0.4 to 1.2 micrometers) of the photo-sensitive composition material. Further, it is desirable that the composition photocure relatively rapidly. The need for thin coatings of a photo-sensitive composition is related to the limited depth of focus of typical exposure patterning equipment and to the minimization of light scatter from the film deposited. The diffusing and spreading effect of the diffraction pattern of the exposing actinic radiation can limit the resolution of fine detail of the photoresist pattern. The very short wavelength of the exposing wavelength of this resist will (proportionately) decrease the width of the diffraction pattern and increase the resolution of fine detail of the resist pattern. In addition, the coating on the surface should be substantially free from pinholes and other blemishes, which would result in defects in the image produced.
Another field in which coatings having very few defects or irregularities are desired is in the field of permselective composite membranes. These are composite membranes which are used for selective separation of components in gases or liquids. Illustrative reverse osmosis membranes are described in U.S. Pat. No. 4,277,344. U.S. Pat. No. 4,704,324 describes preparation of membranes by reaction of onium compounds with nucleophilic compounds and is incorporated herein by reference.
New and improved photocurable coatings suitable for photoresist or membrane applications are desirable. Coatings which cure rapidly with few defects using deep UV radiation and which can be applied from an aqueous solution would be advantageous. These coatings can be used with conventional etchings for manufacture of electronic components and also in membrane applications where chemical stability is of particular importance.
Adhesives are used to bond together organic polymeric components in automobiles and electronic devices. To attain the desired adhesion, polymer surfaces often need to be modified by methods such as chemical etching, electron bombardment and corona discharge. These methods often utilize treatment with chemicals, which may present environmental hazards, produce toxic gases and are inconvenient and expensive. A new and improved method of modifying polymer surfaces is desired.
Fluorocarbon polymers are used in applications that require anti-soiling and oily soil release such as fabrics and cooking utensils. There is a need for a means of applying a photocured or crosslinked fluorocarbon coating to surfaces.